wimax part ii: macjain/cse574-10/ftp/j_bman.pdf · 2012. 10. 2. · part ii: mac raj jain professor...
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11-1©2010 Raj JainCSE574sWashington University in St. Louis
WiMAXWiMAXPart II: MACPart II: MAC
Raj JainProfessor of Computer Science and Engineering
Washington University in Saint LouisSaint Louis, MO 63130
[email protected]/Video recordings of this lecture are available at:
http://www.cse.wustl.edu/~jain/cse574-10/
11-2©2010 Raj JainCSE574sWashington University in St. Louis
Key FeaturesQoS ClassesARQ, Hybrid ARQ (HARQ)Protocol StructurePayload Header SuppressionMAC HeadersScheduling and Link Adaptation
OverviewOverview
11-3©2010 Raj JainCSE574sWashington University in St. Louis
WiMAX MAC: Key FeaturesWiMAX MAC: Key FeaturesFlexible and Extensible - Same MAC for all current and future PHYsModular: Several optional features. Negotiable SS/BS featuresMultiple Topologies: PTP, PMP, meshMultiple Antenna Technologies: Adaptive Antennas, MIMOMultiple Protocol Payloads: ATM, Packets (IP or Ethernet), W or w/o header suppressionFlexible Retransmission Policies: ARQ, HARQTDD and FDD SupportVariety of Subscribers: Several per subscriber or per connection parametersIntegrated QoSSecurity
11-4©2010 Raj JainCSE574sWashington University in St. Louis
Base Station and Subscriber StationsBase Station and Subscriber StationsBase Station (BS): Controls the entire system, frame size, scheduling, admission control, QoS, Ranging, clock synchronization, power control and handoff.
All traffic goes through BSSubscriber Station (SS): Find BS, Acquire PHY synchronization, Obtain MAC parameters, Generate bandwidth requests, make local scheduling decisions, follow transmission/reception schedule from BS, perform initial ranging, maintenance ranging, power controlMobile Station (MS): Mobility management, Handoff, Power Conservation
11-5©2010 Raj JainCSE574sWashington University in St. Louis
Framing and DuplexingFraming and DuplexingBurst = n MPDUs with per burst CRCBurst Profile: Modulation type, FEC, preamble type, guard timeDownlink Interval Usage Code (DIUC): Identifies burst profileDL Channel Descriptor (DCD): Describes DL PHY. Broadcast periodically by BS. Frame duration, Defines DIUCs.Uplink Interval Usage Code (UIUC): Identifies UL burst profilesUL Channel Descriptor (UCD): Describes UL PHY.
11-6©2010 Raj JainCSE574sWashington University in St. Louis
MAP Time RelevanceMAP Time Relevance
DL MAP always refers to current frameUL MAP may be broadcast one frame aheadFDD UL MAP allows for a round-trip delay and MAP processing time
Frame Control
Downlink
Uplink
1 2 3 4Frame #
11-7©2010 Raj JainCSE574sWashington University in St. Louis
Connections and Service FlowsConnections and Service FlowsService Flows = Higher layer flowsEach Service flow has a connectionExtra connections for management and control16-bit CID ⇒ 65,535 connectionsEach station has many connections with BS:
Initial Ranging CIDBasic CIDPrimary Management CIDSecondary Management CID: Higher layerMulticast Polling CID: Bandwidth requests
11-8©2010 Raj JainCSE574sWashington University in St. Louis
IEEE 802.16 IEEE 802.16 –– QoS ClassesQoS ClassesConnection oriented: All traffic is assigned a connectionFive Service Classes:1. Unsolicited Grant Service (UGS): CBR traffic, e.g., voice
Specified throughput, delay, and delay jitter2. Enhanced Real-Time Polling Service (ertPS):
Silence suppressed voice. On/off UGS.3. Real-Time Polling Services (rtPS):
rtVBR, e.g., streaming video. Specified peak and average throughput, delay and delay jitter.
4. Non-Real-Time Polling Service (nrtPS): nrtVBR, e.g., FTP.Specified peak and average throughput
5. Best Effort (BE); No throughput or delay guarantees
11-9©2010 Raj JainCSE574sWashington University in St. Louis
ARQARQAllows selective repeat (Stop and Wait, go back n )ARQ block size negotiated at connection setupDepends upon the Type of Service (ToS), expected delay, etcARQ block cannot be fragmentedA fragment may contain blocks from multiple SDUs
SDU SDUSDU
i i+7i+6i+5i+4i+3i+2i+1
i i+3i+2i+1
MAC PDU
i+4 i+5
MAC PDU
i+6 i+7
MAC PDU
ARQ_BLOCK_SIZE
FSH PSH
11-10©2010 Raj JainCSE574sWashington University in St. Louis
Hybrid (HARQ)Hybrid (HARQ)
Only in OFDMA PHYFour variants (subpackets) of the burst2nd subpacket is sent iff 1st is not received correctly⇒ Stop and Wait with immediate or synchronous acks⇒ Dedicated PHY channel for acksThe receiver tries to decode using both 1st and 2nd
subpacketsProcess continues until success or 4th subpacket
11-11©2010 Raj JainCSE574sWashington University in St. Louis
IEEE 802.16 Protocol StructureIEEE 802.16 Protocol Structure
CS: All functions that are specific to a higher layer protocolClassify SDUs based on MAC address, VLANs, prioritiesAssigns Service Flow ID (SFID) and a connection identifierOptional payload header suppression (PHS)
CPS: Fragmentation and reassembly of large MAC SDUsPacking and unpacking of several small MAC SDUs
Service Specific Convergence Sublayer (CS)MAC Common Part Sublayer (CPS)
Security SublayerPhysical Layer (PHY)PHY
MAC
11-12©2010 Raj JainCSE574sWashington University in St. Louis
IEEE 802.16 Protocol Structure (Cont)IEEE 802.16 Protocol Structure (Cont)
QoS control, Scheduling Bandwidth requestAutomatic repeat request (ARQ)
11-13©2010 Raj JainCSE574sWashington University in St. Louis
Payload Header SuppressionPayload Header Suppression
PHS Fixed = Fixed header bytesPHS Mask = Which bytes?PHS Index = Which rule? Indicates mask and fixed valuesPHS Verify ⇒ Compare before removing
Byte 1 Byte 2 Byte 3 Byte 4 Byte 5 Byte 6 Byte n
11-14©2010 Raj JainCSE574sWashington University in St. Louis
Payload Header Suppression (Cont)Payload Header Suppression (Cont)
11-15©2010 Raj JainCSE574sWashington University in St. Louis
MAC HeadersMAC HeadersGeneric MAC Header: Total 6 bytes per MPDU
HeaderType
EncrypControl
PayloadType
CRCIndicator
EncrypKey #
Len ConnectionIdentifier
HeaderCheck
1b 1b 6b 1b 2b 11b 16b 8b
HeaderType
EncryptionControl
Type: Incremental/Aggregate
BandwidthRequest (Bytes)
CID HCS
1b 1b 3b 11b 16b 8b
Header type: Generic or Stand-alonePayload type bits: Fast Feedback allocation/Grant management,
Packing, Fragmentation, Frag/packing with ARQ, ARQ feedback, MeshBandwidth Request Header: Total 6 bytes
11-16©2010 Raj JainCSE574sWashington University in St. Louis
Fragmentation SubheaderFragmentation SubheaderFragmentation Control: 00=No Frag, 01 Last Frag, 10=First Frag, 11=MiddleFragment Seq #: Mod 8 or mod 2048Block Seq #: Sequence # of the first block in this SDURegular Fragmentation Subheader:
ARQ Fragmentation Subheader
Extended Fragmentation Subheader
Frag Control Frag Seq Num Reserved2b 3b 3b
Frag Control Block Seq Num Reserved2b 11b 3b
Frag Control Frag Seq Num Reserved2b 11b 3b
11-17©2010 Raj JainCSE574sWashington University in St. Louis
Packing SubheaderPacking Subheader
Packing Variable Length SDUs
Packing Fixed Length SDUs
11-18©2010 Raj JainCSE574sWashington University in St. Louis
Grant Management SubheaderGrant Management Subheader
Piggybacked bandwidth requestUGS connections may use UGS-GMSH
Slip indicator: Backlog building up
Non-UGS connections use simple GMSH: No way to indicate incremental/aggregate => Always incremental
Slip Indicator Poll Me Reserved1b 1b 14b
Number of Incremental Bytes Required16b
11-19©2010 Raj JainCSE574sWashington University in St. Louis
Grant Management Header (Cont)Grant Management Header (Cont)
Extended piggyback request: For ertPS class.11 bits of 16-bit header are used for incremental requestIf msb is set, next 4 bits indicate requested polling sizeIf queue builds up SS sets the msb and BS shifts the grant earlier
11-20©2010 Raj JainCSE574sWashington University in St. Louis
Fragmentation, Packing, ConcatenationFragmentation, Packing, ConcatenationFragmentation with or without ARQPacking: Fixed size SDU or variable size SDUConcatenation: Multiple PDUs in a burst
MAC SDU MAC SDU
MACHDR
PACKSHR
MACHDR
FRAGSHR
PACKSHR
MAC PDU MAC PDU
PADMACHDR
MAC PDU
Fragmentation Packing
PHY SDU1 PHY SDU2 PHY SDU3
ConcatenationMAC
PHY
11-21©2010 Raj JainCSE574sWashington University in St. Louis
Fast Feedback Allocation SubheaderFast Feedback Allocation SubheaderRequest feedback from an SS with Advanced Antenna SystemAllocation offset: Number of slots after which the SS should send the feedback (in Ul subframe after 2 frames from now)Feedback type: DL measurement, MIMO feedback, antenna #0, MIMO feedback Antenna #1, MIMO mode
Allocation Offset Feedback Type6b 2b
11-22©2010 Raj JainCSE574sWashington University in St. Louis
ARQ Feedback Information ElementARQ Feedback Information Element
Last ⇒ last in a series of ARQ feedback IEs packed together# Ack Maps: In this IEAck Type:
00=Selective (Starting BSN and Bit map) 01=Cumulative (Ending successful BSN, no bit map) 10=Cumulative with selective (Successful up to BSN and a bit map) 11=cumulative with BSN (1 bit status for n blocks)
CID Last AckType
Block SeqNumber
#AckMaps
AckMap
16b 1b 2b 11b 2b 16b
AckMap
AckMap
16b 16b
11-23©2010 Raj JainCSE574sWashington University in St. Louis
Scheduling and Link AdaptationScheduling and Link AdaptationScheduling:
Base schedules usage of the air link among the subscribers Packet schedulers at the base and subscribers give transmission opportunities to multiple connection queues
Link AdaptationBase determines the contents of the DL and UL portions of each frame Base determines the appropriate burst profile (code rate, modulation level and so on) for each subscriber Base determines the bandwidth requirements of the individual subscribers based on the service classes of the connections and on the status of the traffic queues at the base and subscriber.
11-24©2010 Raj JainCSE574sWashington University in St. Louis
SummarySummary
Centralized resource allocation at base stationGuaranteed QoSEfficient use of available bits
Flexing fragmentation and packingARQ and HARQ
Complex scheduling to provide guarantees under variable conditions
11-25©2010 Raj JainCSE574sWashington University in St. Louis
Related Wikipedia PagesRelated Wikipedia Pageshttp://en.wikipedia.org/wiki/IEEE_802.16#QoShttp://en.wikipedia.org/wiki/Automatic_repeat-requesthttp://en.wikipedia.org/wiki/Hybrid_automatic_repeat_requesthttp://en.wikipedia.org/wiki/Duplex_(telecommunications)http://en.wikipedia.org/wiki/Time-division_duplexhttp://en.wikipedia.org/wiki/Frequency_division_duplex#Frequency-Division_DuplexingSee Part I for books and other Wikipedia pages on WiMAX
11-26©2010 Raj JainCSE574sWashington University in St. Louis
List of AcronymsList of AcronymsARQ Automatic Repeat reQuestBE Best EffortBPSK Binary Phase Shift KeyingBS Base StationBSN Block Sequence NumberCID Connection IdentificationCRC Cyclic Redundancy CheckDCD Downlink Channel DescriptorDIUC Downlink Interval Usage CodeDL DownlinkDSA Dynamic Service AdditionDSC Dynamic Service ChangeDSD Dynamic Service DeleteFDD Frequency Division DuplexingFTP File Transfer ProtocolHARQ Hybrid Automatic Repeat reQuest
11-27©2010 Raj JainCSE574sWashington University in St. Louis
List of Acronyms (Cont)List of Acronyms (Cont)ID IdentificationIEEE Institution of Electrical and Electronics EngineersIP Internet ProtocolMAC Media Access ControlMIMO Multiple Input Multiple OutputMPDU MAC Protocol Data UnitOFDMA Orthogonal Frequency Division Multiple AccessPDU Protocol Data UnitPHS Packet Header SuppressionPHY Physical LayerROHS RObust Header CompressionSDU Service Data UnitSS Subscriber StationUGS Unsolicited Grant ServiceUIUC Uplink Interval Usage CodeUL Uplink